Logical intra mode naming in hevc video coding

ABSTRACT

A method and apparatus of using logical mode numbers during both prediction and coding in the bit stream, such as for high efficiency video coders (HEVC). These logical intra mode numbers are sorted based on angle which as a result leads to improved coding designs with fewer and smaller look-up tables, and a small gain in coding efficiency. Furthermore, by using this type of naming, the number of most probable modes (MPMs) can be readily extended since no additional tables are required. The use of three MPMs achieves a larger gain of 0.25% and 0.31% for the AI_HE and AI_LC cases, respectively.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/674,646 filed on Nov. 12, 2012, incorporated herein by reference inits entirety, which claims priority to, and the benefit of, U.S.provisional patent application Ser. No. 61/589,221 filed on Jan. 20,2012, incorporated herein by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

INCORPORATION-BY-REFERENCE OF COMPUTER PROGRAM APPENDIX

Not Applicable

NOTICE OF MATERIAL SUBJECT TO COPYRIGHT PROTECTION

A portion of the material in this patent document is subject tocopyright protection under the copyright laws of the United States andof other countries. The owner of the copyright rights has no objectionto the facsimile reproduction by anyone of the patent document or thepatent disclosure, as it appears in the United States Patent andTrademark Office publicly available file or records, but otherwisereserves all copyright rights whatsoever. The copyright owner does nothereby waive any of its rights to have this patent document maintainedin secrecy, including without limitation its rights pursuant to 37C.F.R. § 1.14.

BACKGROUND OF THE INVENTION 1. Field of the Invention

This invention pertains generally to video coding, and more particularlyto intra mode naming with high-efficiency video coding devices.

2. Description of Related Art

Currently there are two types intra mode names (numbering) used in HighEfficiency Video Coding (HEVC) test model HM5.0, the logical modenumbers and bit stream mode numbers. Logical mode numbers are moremeaningful and are directly used in the prediction module to produce theintra prediction. In HEVC the logical bit numbers span across verticaldirections VER−8, VER−4, VER, VER+4, VER+8, into the horizontal HOR−4,HOR, HOR+4, which are numbered, with up to 34 prediction directions. Bitstream mode numbers are used to signal the mode to the decoder, and insome implementations, such as HM5.0, may require many look-up tables(e.g., Mode Dependent (MD) coefficient scan, intra smoothing, intraprediction and Mode Dependent (MD) transform) in the programming of thevideo coding device. Bit stream mode numbers were utilized with advancedvideo coding (AVC) coding and considered to be sorted in their frequencyof occurrences. However, statistics collected on High Efficiency VideoCoding (HEVC), do not indicate any bias towards any of the angulardirections (not including Planar and DC), while bypass coding isutilized for the remaining modes.

BRIEF SUMMARY OF THE INVENTION

Logical intra mode naming in High Efficiency Video Coding (HEVC) of thepresent invention utilizes logical mode names and numbering for all modeuses and thus replaces the use of bit stream mode numbers. The logicalmodes have meaningful numbering (naming) for intra modes. It will benoted that in HEVC, a coding unit (CU) may have variable block sizesdepending on video content, and may be split into smaller blocks forprediction as Prediction Units (PU) or transform as Transform Units(TU). Prediction units (PU) can be thought of similarly to partitionsdescribed in other video coding standards, such as the H.264 standard.

When blocks are encoded in intra mode, a prediction block is formedbased on previously encoded and reconstructed blocks adjacent to thecurrent block, the prediction block is configured for being subtractedfrom the current block prior to encoding. There are different predictionmodes for these blocks which define a method of generating a signal frompreviously encoded blocks, for example including prediction types anddirections. Encoders and decoders implemented with high efficiency videocoding utilize both logical mode numbers and bit stream mode numbers. Atthe level of the PUs, intra prediction is performed from samples alreadydecoded in adjacent PUs. Different modes can exist for these PUs,including DC (average), up to 33 angular directions and planar mode.

Using this inventive method, the coding decisions can be simplified byutilizing the same set of logical mode numbers for both prediction andcoding for communication to a decoder. Although the following discussesmaking these decisions in response to the use of look up tables, itshould be appreciated that the simplification is also applicable whenthe decisions are made using other software mechanisms, such asconditional statements, jump tables, pointer references and so forth. Byway of example and not limitation, a number of tables related to intramode coding can be typically eliminated to simplify HEVC encoders anddecoders according to the invention (e.g., eliminating tables:g_aucIntraDirToScanIdx, m_aucIntraFilter, g_aucAngIntraModeOrder,g_aucDCTDSTMode_Hor, g_aucDCTDSTMode_Ver in HM5.0). In addition, designand implementation of fast encoders can be simplified using theselogical intra mode names.

Furthermore, a method is taught herein for utilizing the three MostProbable Modes (MPMs) instead of the two currently used in HEVC coding.It will be appreciated that most probable modes (MPMs) are a mechanismfor optimizing the coding process. More particularly, probabilities areestimated for optimal intra direction as the most probable mode (MPM) ofits neighboring blocks, because current blocks have a strong correlationwith patterns found in neighboring blocks. These MPMs, including thethird MPM, are derived using logical numbering without additional lookup tables. The method of determining multiple most probable modes (MPMs)is shared by both encoder and decoder.

Logical mode numbers according to the invention are utilized for bothperforming prediction and coding in the bit stream. These logical modenumbers are numbered, named or sorted based on angle according to theinvention. For the sake of simplicity of discussion, the following willdescribe these as being mode numbers, although one of ordinary skill inthe art will appreciate that naming and sorting can be similarlyutilized. By way of example, the logical mode numbering is performedwith respect to an arbitrary reference, and these are more beneficiallymeaningful as they result in an improved design with the removal ofseveral otherwise necessary look-up tables. In addition to manysimplifications that result from this type of numbering, simulationsindicate a small coding efficiency benefit. Furthermore, by using thistype of naming, adding an additional MPM is very efficient since noadditional tables are required.

Utilizing the inventive method, fast intra mode decision algorithms canbe simplified. Since modes provide a clear link (association) betweennumbers (names) and angular directions it is easier to apply variousFast Mode Decision (FMD) algorithms, such as utilizing a hierarchicalapproach. In addition, the method can facilitate or simplify otheralgorithms, for example deriving neighboring and perpendicular modes tosimplify algorithms, such as three MPM algorithms. Thus, utilizing anassociation between logical intra mode names and angular directionsallows simplifying decision logic and look-up tables, or elimination ofcertain look-up tables altogether.

The inventive apparatus and method is applicable to video coding devicesimplemented according to the HEVC standard and similar video systemswhich would be enhanced by the intra mode naming taught herein.

Further aspects of the invention will be brought out in the followingportions of the specification, wherein the detailed description is forthe purpose of fully disclosing preferred embodiments of the inventionwithout placing limitations thereon.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

The invention will be more fully understood by reference to thefollowing drawings which are for illustrative purposes only:

FIG. 1 is a schematic of a video encoder using logical intra mode namingaccording to an embodiment of the present invention.

FIG. 2 is a schematic of a video decoder using logical intra mode namingaccording to an embodiment of the present invention.

FIG. 3 is a map of logical intra mode naming according to an embodimentof the present invention, showing directions for each logical name.

FIGS. 4A and 4B are pseudo code instructions of using logical intra modenaming according to an embodiment of the present invention.

FIG. 5 is a flow diagram of an encoding tree for intra mode operationaccording to an embodiment of the present invention.

FIG. 6 is a flow diagram of a decoding tree for intra mode operationaccording to an embodiment of the present invention.

FIGS. 7A and 7B is a flow diagram of determining three MPMs according toan embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention utilizes a form of logical mode numbers, which areenough to describe the directions and which also can be directly codedinto the bit stream instead of using bit stream mode numbers. Using theinventive logical mode numbers throughout the coding system providesmultiple advantages, including the following.

(1) Designs are improved using meaningful mode numbers. Given an intramode number, its directional angle can be determined with simplecalculations without the need of look-up tables. In addition, it can bededuced from the mode numbering that adjacent mode numbers representadjacent prediction directions.

(2) Simple mapping is provided. Using logical mode numbers, a simpleoperation can be performed, for instance clearing the least significantbit in performing mapping for HM5.0, where 4×4 PU has different numberof valid modes from larger PUs. In certain coding systems to avoidmapping, planar mode is utilized for 4×4 PU, whereas an angular modeshould be selected. The invention is also applicable for implementationshaving the same number of modes.

(3) Several look-up tables can be removed utilizing the inventivemethod. In addition, intra smoothing, mode dependent coefficient scan,and mode dependant transform do not require large tables to determinesmoothing filters, scan index, or transform type (DCT/DST). Simple moderange checking is utilized according to at least one embodiment fordetermining the criteria for which different smoothing filters, scans,or transforms can be applied. Furthermore, there is no need for look uptables to convert bit stream mode numbers to logical numbers and viceversa.

(4) Since the mode numbers in the present invention are indicative oftheir angle, design of a fast mode decision for a real time encoder isfar simpler. Also coarse decisions can be reached quickly, for examplefirst testing a lower resolution of the directions and based on thatresult, only modes close to the best one can be tested in the secondstage.

(5) The logical mode numbering makes it simple to compute adjacentdirections. In considering these inventive embodiments, such as thoseinvolving more than two MPMs, directions are utilized which are adjacentto the neighboring intra mode. Coding system implementations accordingto these embodiments can be greatly simplified since the adjacentdirections are computed with simple arithmetic means, such as just byincrementing or decrementing the neighbouring mode number (depending onPU size). The invention also applies in cases having the same numbers ofincrements and decrements.

FIG. 1 illustrates an example embodiment of a coding apparatuscomprising an encoder 10 according to the invention for utilizinglogical intra mode naming (LIMN). The invention is implemented in boththe entropy encoding block 34 and intra prediction block 26, showncontaining generalized logical intra mode naming (LIMN), but otherwisecan rely on conventional video coding which maximizes compatibility withcoding systems. It should be appreciated that other blocks of theencoder may be optimized in response to the inventive teachings.

The encoder 10 is shown with encoding elements 12 executed by one ormore processors 44. In the example, video frame input 14 is shown alongwith reference frames 16 and frame output 18. Inter-prediction 20 isdepicted with motion estimation (ME) 22 and motion compensation (MC) 24.Intra prediction 26 is shown which operates with the logical intra modenaming (LIMN) of the invention and switching is depicted between interprediction and intra prediction. A sum junction 28 is shown with outputto a forward transform 30, operating with Discrete Cosine Transforms(DCT) and/or Discrete Sine Transforms (DST) which are performed based onthe predictions to generate transform coefficients of residual data.Quantization of the transform coefficients is performed at quantizationstage 32, which is followed by entropy encoding 34, which also utilizeslogical intra mode naming (LIMN). Inverse quantization 36 and inversetransform 38 operations are shown coupled to a summing junction 40followed by a filter 42, such as a deblocking and/or loop filter and/orsample adaptive offset.

It should be appreciated that the encoder is shown implemented with aprocessing means 44, such as comprising at least one processing device(e.g., CPU) 46 and at least one memory 48 for executing programmingassociated with the encoding. In addition, it will be appreciated thatelements of the present invention can be implemented as programmingstored on a media, which can be accessed for execution by a CPU for theencoder 10 and/or decoder 50.

FIG. 2 illustrates an example embodiment 50 of a decoder, shown withprocess blocks 52 and an associated processing means 76. It will benoted that the decoder is substantially a subset of the elementscontained in encoder 10 of FIG. 1, operating on reference frames 54,encoded video signal 56 and outputting video 74. Decoder 50 utilizeslogical intra mode naming (LIMN) during entropy decoding and intraprediction, although the information can also be utilized in otherdecoding process steps toward increased efficiency. The decoder blocksreceive an encoded video signal 56 which is processed through entropydecoder 58 which utilizes the inventive logical intra mode naming(LIMN). Following entropy decoding is inverse quantization 60, inversetransform 62, and summing 64 between the inverse transform 62 output andthe selection between inter prediction 66 shown with motion compensation68, and a separate intra prediction block 70. It will be noted thatinter prediction also utilizes the logical intra mode naming (LIMN).Output from summing junction 64 is received by filter 72, which can beconfigured as a loop filter, a deblocking filter, sample adaptiveoffset, or any combination thereof. It should be appreciated that thedecoder can be implemented with a processing means 76 which comprises atleast one processing device 78 and at least one memory 80 for executingprogramming associated with the decoding. In addition, it will be notedthat elements of the present invention can be implemented as programmingstored on a media, wherein said media can be accessed for execution byprocessing device (CPU) 78.

It will be recognized that elements of the present invention 10 and 50are implemented for execution by a processing means 44 and 76, such asin response to programming resident in memory 48 and 80 which isexecutable on computer processor (CPU) 46 and 78. In addition, it willbe appreciated that elements of the present invention can be implementedas programming stored on a media, wherein said media can be accessed forexecution by CPU 46 and 78.

It should be appreciated that the programming is executable from thememory which is a tangible (physical) computer readable media that isnon-transitory in that it does not merely constitute a transitorypropagating signal, but is actually capable of retaining programming,such as within any desired form and number of static or dynamic memorydevices. These memory devices need not be implemented to maintain dataunder all conditions (e.g., power fail) to be considered herein asnon-transitory media.

FIG. 3 illustrates an example embodiment of intra mode numberingutilized according to an embodiment of the present invention, showing asimple monotonic sequence, exemplified with sequential numbering from 2through 34, whose angles pass through various horizontal, up-rightdiagonal scan (shown as up-right scan for brevity) and vertical scans.Direction 0 represents Planar, and 1 represents DC, which are not shownin the figure.

It should be appreciated that a function based on a subset of realnumbers with real values is called monotonic, if all x and y with x≤yhas f(x)≤f(y) for monotonically increasing, or with x≥y for f(x)≥f(y)for monotonically decreasing, thereby preserving the order. Embodimentsof the present invention can be implemented with any desired alternativenumber sequences, in particular monotonic number sequences, withoutdeparting from the teachings of the present invention. It should beappreciated that the index of the scan can be easily derived bycalculating the distance of the mode from vertical and horizontaldirections. Therefore, the look-up table g_aucIntraDirToScanIdx[MAX_CU_DEPTH][NUM_INTRA_MODE] can be removed.

Similarly, in intra mode smoothing, the angular offset from bothhorizontal and vertical can be readily determined in response tonumerical displacement, such as utilizing simple comparisons by additionand subtraction from logical intra mode naming. Thus, intra modesmoothing is performed in response to the amount of angular differencefound between logical intra mode names (which represent angular offsetsfrom horizontal and/or vertical). For example, with the minimum of thesenumerical displacements compared against a pre-determined value storedin a much smaller look-up table, such as of size 5 rather than 5×36array in current test model of HEVC (HM5.0). If the minimum numericaldisplacement (angular difference) is larger than the value of the tablefor the corresponding block size, then smoothing is applied. Therefore,the table can be reduced from m_aucIntraFilter[5][NUM_INTRA_MODE] tom_aucIntraFilter[5]={10, 7, 1, 0, 10}. A value of 10 is sufficientlylarge to prevent smoothing from being applied to any intra mode for thatblock size. Using this table, the modes for which smoothing is appliedare exactly the same as HEVC test model HM 5.0, yet the table size isreduced.

In coding systems in which mode dependent transforms are based on intramodes, the tables for mode dependent transforms (e.g., Discrete SineTransforms and Discrete Cosine Transforms (DST and DCT)), can also beremoved in a similar fashion, in view of using the logical mode numbers.For a two dimensional 4×4 transform, a one dimensional verticaltransform is followed by a one dimensional horizontal transform. Thevertical DST is applied to the planar mode and to modes 11 through 34for vertical transform. The remainder of the modes use vertical DCTtransform. Horizontal DST is, on the other hand, applied to planar modeand to modes 2 through 25 for horizontal transform. The remainder of themodes use the horizontal DCT transform, whereby tablesg_aucDCTDSTMode_Hor and g_aucDCTDSTMode_Vert in HM5.0 can be safelyremoved. It will be noted that both horizontal and vertical DST areperformed for the planar mode. The invention can be similarlyimplemented in cases when a single transform is applied regardless ofintra mode.

In addition, in response to using this form of logical mode numbers,instead of bit stream mode naming, the table which maps logical and bitstream numbers, such as g_aucAngIntraModeOrder [NUM_INTRA_MODE] inHM5.0, is no longer necessary.

The present invention can be extended to any desired number of MostProbable Modes (MPMs), the following example describing extension tothree MPMs. In certain HEVC coding systems there are 35 intra modes for8×8, 16×16, and 32×32 PU sizes, while 4×4 PUs however, consider only 18modes. The rationale is to have the number of modes as a structure with3 MPMs+x, where x is the number of remaining modes. The presentinvention, thus provides a full symmetric approach with no gain in whichx is a power of two. So in a 4×4 the value of x is 16, while in others xis equal to 32. With this full symmetric approach, there are 19 and 35modes for 4×4 and larger PUs (e.g., 8×8/16×16/32×32), respectively,which corresponds to 3 modes in addition to a full power of 2.Consequentially, if 3 MPMs are allowed, there will be exactly 16 and 32remaining modes for 4×4 and larger (e.g., 8×8/16×16/32×32) PUs,respectively, thus eliminating the need of any escape codes that arecurrently needed in the software design.

It should be noted that the introduction of a third MPM adds noadditional complexity or memory-context requirements. The 3 MPMs arederived using simple operations without any look-up tables as seen inTable 1 in which the value of δ is 2 for 4×4 PUs and 1 for the rest ofthe PU sizes in HM 5.0 and the value can vary in general. One ofordinary skill in the art will appreciate that the values of δ and thelook up tables can be implemented in various alternative ways withoutdeparting from the teachings of the invention. It should be appreciatedthat the table basically indicates how to set MPMs from neighboringblocks, as seen in more detail in FIG. 4A and FIG. 4B, described in alater section.

Implementing the inventive elements into an HEVC coding system (e.g.,test model HM 5.0) can provide a number of benefits. For regularity, 19luma intra prediction modes are assumed for 4×4 PUs as mentioned in theprevious section. This additional mode, however, has no additional gain(as verified by other contributions) and is merely added for the sake ofsymmetry and improved design. A small gain was found in BD-rateperformance based on the use of the intra mode renaming, the small gaindue to improved mapping from 35 modes to 19 modes in 4×4 PUs, aspreviously described. If 3 MPM is utilized, the BD-rate performance withthe inventive 3-MPM method under the common test condition are improved,as seen in Table 2. It should be noted that no additional context isdefined even for the case of 3 MPMs.

FIG. 4A and FIG. 4B illustrate MPM derivation according to theinvention, shown as generalized pseudo-code. In FIG. 4A the decisionsare shown for the condition if iLeftIntraDir is equal to iAboveIntraDir,while in FIG. 4B decisions are otherwise shown for when iLeftIntraDir isnot equal to AboveIntraDir. These are described in a more readilyunderstood form in FIG. 5 and FIG. 6, respectively.

FIG. 5 illustrates an intra mode encoding tree for the intra predictionmode 90 of the invention. A determination 92 is made if the intraprediction is equal to one of MPMs. If not equal to any of MPMs then azero is encoded 94, after which encoding is performed 96 withfixed-length codes for the remaining modes. Otherwise, for MPMs thefirst bit is encoded 100 as a one. A determination is then made 102 ifthe mode is MPM0. If it is MPM0 then a zero is encoded 104. If not MPM0then a 1 is encoded 106, and a determination is made 108 if the mode isMPM1. If it is MPM1 then a zero is encoded 110, and if not MPM1 modethen a one is encoded 112. In any case the bits are inserted in the bitstream for intra mode 98. Even though it seems preferable to performchecking in the order of MPM0, MPM1 and MPM2, one of ordinary skill inthe art will appreciate that the sequence of encoding for MPMs, MPM0 andMPM1 can be selected in any desired order and/or the selection of onesand zeros in the above example scenario can be reversed, withoutdeparting from the teachings of the present invention. In particular,programming executable on said processor encodes a first bit in a firststate indicating that the intra mode is not equal to any of the MPMs,wherein all encoding is according to fixed-length codes for theremaining modes. Alternatively, the first bit is encoded in a secondstate, inverse to said first state, to indicate that the intra mode isequal to one of the MPMs, whereby subsequent bits after the first bitindicate if MPM0, MPM1 or MPM2 is selected.

FIG. 6 illustrates an intra mode decoding tree for the invention with abit stream 130. The first bit is decoded 132, and if it is zero, thenfixed length codes are to be decoded for the remaining modes at block134, and decoded fixed-length code is mapped to intra mode 136, andintra prediction mode is determined 138. If the first decoded bit is aone, then at block 140 the next bit is decoded, and if it is zero MPM0142 is selected, if one, then block 144 decodes the next bit. If thisthird bit is a zero, then MPM1 146 is selected, and if a one, then MPM2148 is selected, all of which continue with determining intra predictionmode 138.

FIG. 7A and FIG. 7B illustrates an example embodiment of determining 3MPMs, as utilized in both the encoder and decoder to assist encoding anddecoding of intra prediction modes. In decision 150, the valueiLeftIntraDir is set to the intra prediction mode of left neighboring PUin block 152 if left neighboring PU is intra coded (mode), otherwiseiLeftIntraDir is set to DC in block 154. In decision 156 the valueiAboveIntraDir is set to the intra prediction mode of above neighboringPU in block 158 if above neighboring PU is intra coded, otherwiseiAboveIntraDir is set to DC in block 160. Using iLeftIntraDir andiAboveIntraDir 162, if these are not equal in block 164, then in block166 a check is made to see if any one is planar. If not planar then MPM0is set to iLeftIntraDir mode, MPM1 set to iAboveIntraDir mode, and MPM2set to Planar mode in block 168. If any are planar, then block 170determines if the other is DC. If it is not DC, then in block 172 MPM0is set to iLeftIntraDir, MPM1 is set to iAboveIntraDir, and MPM2 is setto DC. If the other is DC, then at block 174 MPM0 is set toiLeftIntraDir, MPM1 is set to iAboveIntraDir, and MPM2 is set toVertical. Returning to block 164, if iLeftIntraDir is equal toiAboveIntraDir then block 176 checks if iLeftIntraDir is angular. Fornon-angular iLeftIntraDir at block 178 MPM0 is set to Planar, MPM1 isset to DC, and MPM2 is set to Vertical. For angular iLeftIntraDir atblock 180 MPM0 is set to iLeftIntraDir, MPM1 is set to iLeftIntraDir−δ,and MPM2 is set to iLeftIntraDir+δ, where the value of δ is 2 for 4×4PUs and 1 for the rest of the PU sizes in HM5.0. Again, one of ordinaryskill in the art will recognize that differing values may be utilizedwithout departing from the teachings of the present invention.

Embodiments of the present invention may be described with reference toflowchart illustrations of methods and systems according to embodimentsof the invention, and/or algorithms, formulae, or other computationaldepictions, which may also be implemented as computer program products.In this regard, each block or step of a flowchart, and combinations ofblocks (and/or steps) in a flowchart, algorithm, formula, orcomputational depiction can be implemented by various means, such ashardware, firmware, and/or software including one or more computerprogram instructions embodied in computer-readable program code logic.As will be appreciated, any such computer program instructions may beloaded onto a computer, including without limitation a general purposecomputer or special purpose computer, or other programmable processingapparatus to produce a machine, such that the computer programinstructions which execute on the computer or other programmableprocessing apparatus create means for implementing the functionsspecified in the block(s) of the flowchart(s).

Accordingly, blocks of the flowcharts, algorithms, formulae, orcomputational depictions support combinations of means for performingthe specified functions, combinations of steps for performing thespecified functions, and computer program instructions, such as embodiedin computer-readable program code logic means, for performing thespecified functions. It will also be understood that each block of theflowchart illustrations, algorithms, formulae, or computationaldepictions and combinations thereof described herein, can be implementedby special purpose hardware-based computer systems which perform thespecified functions or steps, or combinations of special purposehardware and computer-readable program code logic means.

Furthermore, these computer program instructions, such as embodied incomputer-readable program code logic, may also be stored in acomputer-readable memory that can direct a computer or otherprogrammable processing apparatus to function in a particular manner,such that the instructions stored in the computer-readable memoryproduce an article of manufacture including instruction means whichimplement the function specified in the block(s) of the flowchart(s).The computer program instructions may also be loaded onto a computer orother programmable processing apparatus to cause a series of operationalsteps to be performed on the computer or other programmable processingapparatus to produce a computer-implemented process such that theinstructions which execute on the computer or other programmableprocessing apparatus provide steps for implementing the functionsspecified in the block(s) of the flowchart(s), algorithm(s), formula(e),or computational depiction(s).

From the discussion above it will be appreciated that the invention canbe embodied in various ways, including the following:

1. An apparatus for encoding and decoding video signals, comprising: (a)a video encoder having a computer processor; (b) programming executableon said video encoder computer processor for: (i) selecting intraprediction types and modes in a prediction unit and encoding withlogical intra mode naming each said mode having a mode number, whereineach mode number in said logical intra mode naming is associated with anangular direction as a monotonic sequence including representations forDC mode, planar mode, and a plurality of directions, and utilizing saidlogical intra mode naming for decisions made during intra prediction andentropy encoding; and (ii) deriving a scan index from said intra modenaming by calculating distance of each said mode from vertical andhorizontal directions for use in making said decisions during intraprediction and entropy encoding; (c) a video decoder having a computerprocessor; and (d) programming executable on said video decoder computerprocessor for receiving from said video encoder most probable modes(MPMs) and intra prediction types and modes, and utilizing logical intramode naming (LIMN) for making decisions during entropy decoding andintra prediction.

2. The apparatus of any preceding embodiment, wherein said video encoderand said video decoder are configured for high efficiency video coding(HEVC), utilizing coding units (CUs) having variable block sizesdepending on video content, which are split into smaller blocks forprediction as Prediction Units (PUs) or transform as Transform Units(TUs).

3. The apparatus of any preceding embodiment, wherein said plurality ofdirections represent directions spanning through horizontal scans,up-right diagonal scans and vertical scans.

4. The apparatus of any preceding embodiment, further comprisingprogramming executable on said video encoder computer processor fordetermining multiple most probable modes (MPMs) of intra mode directionsfor communication to the decoder.

5. An apparatus for video encoding, comprising: (a) a video encoderhaving a computer processor; and (b) programming executable on saidcomputer processor for: (i) selecting intra prediction types and modesof a prediction unit (PU); (ii) encoding said prediction types and modesof the prediction units using logical intra mode naming in which eachmode has a mode number that is associated with an angular direction as amonotonic sequence including representations for DC mode, planar mode,and a plurality of directions, and (iii) outputting said logical intramode naming for use by a decoder in determining prediction types andmodes based on said logical intra mode naming

6. The apparatus of any preceding embodiment, wherein said video encoderis a high efficiency video coding (HEVC) encoder, utilizing coding units(CUs) having variable block sizes depending on video content, which aresplit into smaller blocks for prediction as Prediction Units (PUs) ortransform as Transform Units (TUs).

7. The apparatus of any preceding embodiment, wherein said plurality ofdirections represent directions spanning through horizontal scans,up-right diagonal scans and vertical scans.

8. The apparatus of any preceding embodiment, wherein said programmingexecutable on said computer processor is configured to utilize anassociation between logical intra mode names and angular directions tosimplify decision logic and look-up tables.

9. The apparatus of any preceding embodiment, wherein said look-uptables are selected from the group of tables consisting of intraprediction, intra smoothing, mode dependent coefficient scan and modedependent transform.

10. The apparatus of any preceding embodiment, further comprisingprogramming executable on said computer processor for encoding mostprobable modes (MPMs) of intra mode directions.

11. The apparatus of any preceding embodiment, further comprisingprogramming executable on said computer processor for encoding a firstbit in a first state indicating that intra prediction mode is not equalto any MPMs, wherein all encoding is according to fixed-length code forremaining modes; and encoding said first bit in a second state, inverseto said first state, indicating that intra prediction mode is equal toone of MPMs, with subsequent bits after said first bit indicating ifMPM0, MPM1 or MPM2 is selected.

12. The apparatus of any preceding embodiment, further comprisingprogramming executable on said computer processor for performingprediction at the prediction unit (PU) level, from samples alreadydecoded in adjacent prediction units (PUs).

13. The apparatus of any preceding embodiment, further comprisingprogramming executable on said computer processor for executing intramode smoothing in response to the amount of angular difference betweenlogical intra mode names.

14. The apparatus of any preceding embodiment, further comprisingprogramming executable on said computer processor for applying smoothingif amount of angular difference is larger than the value of a table fora corresponding block size.

15. The apparatus of any preceding embodiment, further comprising:programming executable on said computer processor for processing a twodimensional 4×4 transform as a one dimensional vertical transformfollowed by a one dimensional horizontal transform; wherein directionalmodes have values of 2 through 34; wherein a vertical discrete sinetransform (DST) is applied to the planar mode and to modes 11 through 34for vertical transform, with remaining modes using vertical discretecosine transform (DCT); and wherein a horizontal DST is applied toplanar mode and to modes 2 through 25 for horizontal transform.

16. An apparatus for decoding video signals, comprising: (a) a decoderhaving a computer processor configured for decoding video frames; and(b) programming executable on said computer processor for: (i) receivingintra prediction types and modes and most probable modes (MPMs) forprediction units (PUs) utilizing logical intra mode naming (LIMN) froman encoder; (ii) wherein each logical mode number is associated with anangular direction as a monotonic sequence whose numbers includerepresentations for DC mode, planar mode, and a plurality of directions;and (iii) making entropy decoding and intra prediction decisions basedon received values encoded with logical intra mode naming (LIMN).

17. The apparatus of any preceding embodiment, wherein said videodecoder is a high efficiency video coding (HEVC) encoder, utilizingcoding units (CUs) having variable block sizes depending on videocontent which are split into smaller blocks for prediction as PredictionUnits (PUs) or transform as Transform Units (TUs.

18. The apparatus of any preceding embodiment, further comprisingprogramming executable on said computer processor for decoding three ofsaid most probable modes (MPMs) as received from an encoder.

19. The apparatus of any preceding embodiment, further comprisingprogramming executable on said computer processor for decoding a firstbit that in a first state indicates that intra prediction mode is notset to any MPMs wherein all encoding is according to fixed-length codefor remaining modes; and decoding said first bit in a second state,inverse to said first state, which indicates that intra prediction modeis equal to one of MPMs, with subsequent bits after said first bitindicating if MPM0, MPM1 or MPM2 is selected.

20. The apparatus of any preceding embodiment, further comprising:programming executable on said computer processor for processing a twodimensional 4×4 transform as a one dimensional vertical transformfollowed by a one dimensional horizontal transform; wherein directionalmodes have values of 2 through 34; wherein a vertical discrete sinetransform (DST) is applied to the planar mode and to modes 11 through 34for vertical transform, with remaining modes using vertical discretecosine transform (DCT); and wherein a horizontal DST is applied toplanar mode and to modes 2 through 25 for horizontal transform.

Although the description above contains many details, these should notbe construed as limiting the scope of the invention but as merelyproviding illustrations of some of the presently preferred embodimentsof this invention. Therefore, it will be appreciated that the scope ofthe present invention fully encompasses other embodiments which maybecome obvious to those skilled in the art, and that the scope of thepresent invention is accordingly to be limited by nothing other than theappended claims, in which reference to an element in the singular is notintended to mean “one and only one” unless explicitly so stated, butrather “one or more.” All structural and functional equivalents to theelements of the above-described preferred embodiment that are known tothose of ordinary skill in the art are expressly incorporated herein byreference and are intended to be encompassed by the present claims.Moreover, it is not necessary for a device or method to address each andevery problem sought to be solved by the present invention, for it to beencompassed by the present claims. Furthermore, no element, component,or method step in the present disclosure is intended to be dedicated tothe public regardless of whether the element, component, or method stepis explicitly recited in the claims. No claim element herein is to beconstrued as a “means plus function” element unless the element isexpressly recited using the phrase “means for”. No claim element hereinis to be construed as a “step plus function” element unless the elementis expressly recited using the phrase “step for”.

TABLE 1 Derivation of 3 MPMs Neighbouring modes condition MPMs (threeMPMs) iLeftIntraDir == iAboveIntraDir iLeftIntraDir, iLeftIntraDir− δ,iLeftIntraDir+ δ iLeftIntraDir != iAboveIntraDir iLeftIntraDir,iAboveIntraDir, Planar/DC

TABLE 2 Results for Intra Mode Name Modification for 3MPM All Intra HEAll Intra LC Y U V Y U V Class A (8bit) −0.29% −0.13% 0.00% −0.38%−0.15% −0.09% Class B −0.20% −0.07% −0.06% −0.28% −0.07% −0.06% Class C−0.25% −0.13% −0.16% −0.32% −0.17% −0.18% Class D −0.21% −0.07% −0.09%−0.24% −0.10% −0.13% Class E −0.33% −0.25% −0.05% −0.42% −0.13% −0.15%Overall −0.25% −0.12% −0.08% −0.31% −0.12% −0.12% −0.25% −0.13% −0.08%−0.31% −0.12% −0.13% Class F −0.33% −0.35% −0.28% −0.33% −0.38% −0.45%Enc Time [%] 100% 100% Dec Time [%] 100% 100%

1. (canceled)
 2. An image processing apparatus, comprising: a memoryconfigured to store instructions; and a processor configured to executethe instructions stored in the memory, wherein the processor is furtherconfigured to: set candidate intra prediction modes based on adetermination that (A) a first intra prediction mode for a leftneighboring block adjacent to a current block is unequal to a secondintra prediction mode for an above neighboring block adjacent to thecurrent block, and (B) both the first intra prediction mode and thesecond intra prediction mode are not planar prediction; and performintra prediction based on a third intra prediction mode selected fromthe candidate intra prediction modes, wherein the set of the candidateintra prediction modes comprises set a mode number that indicates thecandidate intra prediction modes, and wherein mode number 0 indicatesthe first intra prediction mode, mode number 1 indicates the secondintra prediction mode, and mode number 2 indicates the planarprediction.
 3. The image processing apparatus of claim 2, wherein theprocessor is further configured to: obtain the mode number from a bitstream; and set the third intra prediction mode from the candidate intraprediction modes based on the mode number that is obtained from the bitstream.
 4. The image processing apparatus of claim 2, wherein the leftneighboring block and the above neighboring block are Transform Units.5. The image processing apparatus of claim 2, wherein the leftneighboring block and the above neighboring block are Prediction Units.6. The image processing apparatus of claim 2, wherein the candidateintra prediction modes are intra prediction modes from most probablemodes (MPMs).
 7. A method, comprising: in an image processing apparatus:setting candidate intra prediction modes based on a determination that(A) a first intra prediction mode for a left neighboring block adjacentto a current block is unequal to a second intra prediction mode for anabove neighboring block adjacent to the current block, and (B) both thefirst intra prediction mode and the second intra prediction mode are notplanar prediction; and performing intra prediction based on a thirdintra prediction mode selected from the candidate intra predictionmodes, wherein the setting of the candidate intra prediction modescomprises set a mode number that indicates the candidate intraprediction modes, and wherein mode number 0 indicates the first intraprediction mode, mode number 1 indicates the second intra predictionmode, and mode number 2 indicates the planar prediction.
 8. The methodof claim 7, further comprising: obtaining the mode number from a bitstream; and setting the third intra prediction mode from the candidateintra prediction modes based on the mode number that is obtained fromthe bit stream.
 9. The method of claim 7, wherein the left neighboringblock and the above neighboring block are Transform Units.
 10. Themethod of claim 7, wherein the left neighboring block and the aboveneighboring block are Prediction Units.
 11. The method of claim 7,wherein the candidate intra prediction modes are intra prediction modesfrom most probable modes (MPMs).